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A Self-Propelled Artillery Walker (SPHA) had twelve legs that served as mobile support structures. Unlike smaller walkers, such as the AT-TE, SPHA units were unable to be carried into battle by LAAT/c gunships because of their large size and weight. Instead, they were deployed directly from landed Acclamator-class assault ships, which could carry 36 of the artillery platforms.[1]

In battle, SPHA walkers usually received orders from ground-based command posts, which provided a less isolated and more in-touch view of the battlefield than the towering walkers. In addition, SPHA units had a complement of 30 clone troopers, which could be deployed rapidly via a dorsal hatch. In seconds, the soldiers could disembark the vehicle and secure the area immediately around the walker, providing protection from enemy infantry and other light units.

The SPHA walker chassis served as the basis for a number of different weapons platforms, though the best chronicled version was the turbolaser (SPHA-T) configuration. This variant's main weapon was a heavy turbolaser cannon, capable of causing extreme direct fire damage to large or slow-moving targets.[5] The turbolaser boasted tremendous range and was capable of penetrating deflector shields.[3]

The primary disadvantage of this powerful weapon was that it was incapable of providing indirect fire support to out of sight locations, a problem remedied in other models. Another disadvantage was that the weapon could only be charged to a certain level—upon firing such shots, they had to be replaced with charged guns from the rear lines.[7]

It complemented the two other key components of Republic military strategy—the AT-TE walker and the LAAT/igunship. In a typical attack, the AT-TEs and LAATs would spearhead the assault, establishing a forward base and allowing heavier support forces (such as SPHA walkers) to consolidate gains and provide reinforcements.[source?]

The power usage of the turbolaser cannon in the SPHA-T variant dictated the design of the other parts of the vehicle.[5]

Designers rejected a complex turret mechanism, instead relying on the entire walker to reposition in order to adjust for different firing coordinates.[5] Because of the fixed weapon positioning, as well as the slow firing speed of the turbolaser, the SPHA was unable to track rapidly moving targets, such as speeders or small atmospheric craft.[source?] Like other walkers, the use of articulated legs prevented the SPHA from being vulnerable to anti-repulsorlift weapons, at the cost of some mobility.[5]

The result of this development process was a walker that possessed a very capable capital ship-class weapon, but was hampered by its low mobility. This low mobility was exacerbated by the fact that SPHA walkers were equipped with heavy armor, especially in the frontal area of the vehicle around and just below the command deck. This armor was necessary to protect the vehicle's reactor core from enemy fire, as any meltdown, and subsequent explosions, would cause tremendous collateral damage.[source?]

The Galactic Empire later developed a more compact version, the SPMA, which was more mobile and compact, thanks to weight-reducing advancements in technology.[8]

The SPHA-line walkers continued in service in the early years of the Galactic Empire, until the SPMA-line was developed, with the SPMA vehicles being faster and more maneuverable than the cumbersome SPHA-Ts.[8]

Concept art of the SPHA-T was drawn by Concept Design Supervisor Erik Tiemens. He initially imagined a treaded vehicle, but George Lucas changed it to a walker. The SPHA's production name was "Clone Tank A".[5]